As more and more computers are interconnected through various networks, such as the Internet, computer security also becomes increasingly more important. In particular, computer security in regard to external attacks from malware has become, and continues to become, increasingly more important. Malware, for purposes of the present discussion, is defined as unwanted computer attacks. Those skilled in the art will appreciate that malware includes, but is not limited to, computer viruses, Trojan horses, worms, denial of service attacks, abuse/misuse of legitimate computer system functions, and the like. The primary defense against malware is anti-virus software.
FIGS. 1A and 1B are pictorial diagrams illustrating how anti-virus software currently operates. In particular, FIG. 1A illustrates how anti-virus software detects known malware and prevents the known malware from reaching and infecting a computer. Alternatively, FIG. 1B illustrates a common weakness of anti-virus software, particularly how anti-virus software is unable to detect and prevent modified malware from reaching and infecting a computer. What is meant by “reaching” the computer is getting past the anti-virus software. Those skilled in the art will readily recognize anti-virus software almost always resides on the computer it is protecting, and operates on incoming data as it physically arrives at the computer. Thus, while incoming data, including malware, may be located at the computer, for purposes of the present invention, the incoming data does not actually “reach” the computer until it gets past the anti-virus software.
As shown in FIG. 1A, malware 102 is directed over a network 106 to the computer 110, as indicated by arrow 108. Those skilled in the art will appreciate that the malware 102 may be directed to the computer 110 as a result of a request from the computer, or directed to the computer from another network device. However, before the known malware 102 infects the computer 110, anti-virus software 104, which is typically installed on the computer 110, intercepts the malware and examines it. The anti-virus software scans the incoming data (malware) as a file, searching for identifiable patterns, also referred to a signatures, associated with known malware. If a malware signature is located in the file, the anti-virus software 104 takes appropriate action, such as deleting the known malware/infected file, or removing the malware from an infected file, sometimes referred to as cleaning the file. In this manner, anti-virus software 104 is able to prevent the known malware 102 from reaching and infecting the computer 110, as indicated by the arrow 112.
Those skilled in the art will appreciate that almost all unknown malware are actually rewrites or reorganizations of previously released malware. Indeed, encountering an absolutely novel malware is relatively rare, as most “new” malware are actually rewrites or rehashes of existing malware. Malware source code is readily available and it is a simple task for a malicious party to change variable names, reorder lines of code, or somehow superficially modify the malware. This is especially true with script-based malware, as scripts are essentially text files that are interpreted by a script processor/interpreter on a host computer.
The end result of rehashing or rewriting an existing malware is that the static appearance of the malware is superficially altered while the functionality of the malware typically remains the same. Unfortunately, current anti-virus software operates only on the static signatures of known malware. Thus “new” malware, while it may functionally identical to its “parent” malware, is not detected nor stopped by current anti-virus software 104 due to the pattern matching system of the anti-virus software.
FIG. 1B is a pictorial diagram illustrating how current anti-virus software is unable to prevent a modified malware from reaching a computer. As shown in FIG. 1B, known malware 102 undergoes a modification process 114, such as a rehash or rewrite, resulting in modified malware 116. As mentioned above, the modified malware 116 will most likely have a different static appearance, though its functionality may be the same. As mentioned above, because the static appearance is modified, the modified malware 116 is not a “known” malware to the anti-virus software 104.
The modified malware 116 is directed through the network 106 to the computer 110, as indicated by arrow 118. As described above, the anti-virus software 104 attempts to identify the modified malware 116 to determine whether it is known malware and should be stopped. As the modified malware 116 is, as yet, an unknown modification, and because the signature of the modified malware is not the same as the original malware 102, the anti-virus software 104 fails to identify the modified malware 116 as malware, and permits it to proceed to the computer 110, as indicated by arrow 120. Upon reaching the computer 110, the modified malware 116 is able to perform its destructive purpose. It is only after an anti-virus software provider identifies a signature pattern for the modified malware 116 and then updates the anti-virus software 104, that the anti-virus software 104 is able to protect the computer 110 from the modified malware 116.
Constantly evaluating unknown malware to identify a static signature and then updating anti-virus software with the new signature is a costly process. It is also inefficient, especially when considering that the modified malware 116 is only superficially modified from its parent, i.e., the known malware 102. It would be helpful if the malware could be identified, not just by its static signature, but also by its functionality. However, currently the only way to evaluate the functionality of malware is to permit it to execute on a computer 110. Of course, this is entirely unacceptable as the ill effects of the malware would run its course on the computer.
In light of the above-identified problems, what is needed is a system and method for evaluating the functionality of an executable script to determine whether the executable script is malware without actually executing the script on the computer. The system and method should also operate in addition to, or separately from, current anti-virus software to protect a computer against rewritten or reorganized malware scripts. The present invention addresses this and other issues found in the prior art.